Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., single layer core and single layer cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover.
Examples of golf ball materials range from rubber materials, such as balata, styrene butadiene, polybutadiene, or polyisoprene, to thermoplastic or thermoset resins such as ionomers, polyolefins, polyamides, polyesters, polyurethanes, polyureas and/or polyurethane/polyurea hybrids, and blends thereof. Typically, outer layers are formed about the spherical outer surface of an innermost golf ball layer via compression molding, casting, or injection molding.
From the perspective of a golf ball manufacturer, it is desirable to have materials exhibiting a wide range of properties, such as resilience, durability, spin, and “feel,” because this enables the manufacturer to make and sell golf balls suited to differing levels of ability and/or preferences. In this regard, playing characteristics of golf balls, such as spin, feel, CoR and compression can be tailored by varying the properties of the golf ball materials and/or adding additional golf ball layers such as at least one intermediate layer disposed between the cover and the core. Intermediate layers can be of solid construction, and have also been formed of a tensioned elastomeric winding. The difference in play characteristics resulting from these different types of constructions can be quite significant.
In one approach, a “stiffer, as opposed to springy” material was produced by stretching cross-linked polymeric bands, skins or bladders and applying same over or about a core. See, e.g., U.S. Pat. No. 6,042,489 of Renard et al. at Col. 2, ll. 24-26. The cross-linked material crystalized under the mechanical tension or strain of stretching and resulted in the stiffer material. See, e.g., Mechanically-Induced chemical Changes in Polymeric Materials, Caruso et al, Chem. Rev., Oct. 14, 2009 at § 3.2.1.
However, since there are golfers who prefer a springy rather than stiff feel off the tee, there is still a need for materials that can achieve benefits from stretching without inducing crystallinity within the polymer network. Golf balls of the present invention address and solve this need.